1. Field of the Invention
The present invention relates to a method of non-destructively inspecting ceramic members such as gas turbine blades, burners, walls flame sprayed with ceramics for a nuclear fusion reactor, tiles of a space shuttle, and the like to estimate the life expectancy of the members.
2. Description of the Related Art
An attempt has been made to make gas turbines workable at higher temperatures in order to improve the electricity generation efficiency of the gas turbines. Such increase in temperature requires a member having a higher thermal resistance and there have been utilized gas turbine members having an adiabatic layer flame sprayed with ceramics.
It is necessary to know the life of these gas turbine members, for example, gas turbine blades and it is also desired that the inspection of the members for determining the life expectancy thereof be accomplished at a lower cost as well as in a possibly shortest break down time of the gas turbines. The estimation of the life of turbine blades has been made heretofore by cutting off a part of the ceramic coating layer formed on the gas turbine blades by a flame spraying method and directly inspecting the grain growth of the surface layer of the heat resistant metal substrate.
The prior art inspection as above suffers from the necessity for fracturing partly ceramic members such as turbine blades every time when the periodical inspection is effected and the considerably long time required for the inspection to be completed. In addition to the problem that the ceramic coating layer must be removed out of the turbine blade substrate, there has not been established a method of predicting the expected life to the time when actual release of the coatings occurs. Moreover, there is a problem that the conventional inspection process will not be able to apply when the whole turbine blade becomes made of ceramics in future.